Manufacture of cBN by the high pressure/high temperature (HP/HT) process is known in the art and explained in U.S. Pat. No. 2,947,617. A process for making sintered polycrystalline cBN compacts, which utilizes pyrolytic hexagonal boron nitride (PBN) in the absence of a catalyst is described in U.S. Pat. No. 4,1888,194. An improvement on such direct conversion process is described in U.S. Pat. No. 4,289,503, where boric oxide is removed from the surface of the HBN powder before the conversion process.
A compact as used in the cutter art comprises a mass of abrasive particles bonded together in a self-bonded relationship, by means of a bonding medium, or by means of combinations thereof. A composite compact is a compact bonded to a substrate material, such as cemented metal carbide. U.S. Pat. No. 3,918,219 describes the catalytic conversion of hexagonal boron nitride (HBN) to cBN in contact with a carbide mass to form a composite cBN compact. Compacts or composite compacts may be used in blanks for cutting tools, drill bits, dressing tools, and wear parts